Treatment of rubber



res PATENT oFFicB TREATMENT OF RUBBER Ernest E. Curtis, Yonkers, N. Y., assignor to United States Rubber Products, Inc., New York, N. Y., a corporation of Delaware No Drawing. Application August 27, 1935,

I Serial No. 38,061; y

6 Claims. (Cl. 91-68) This invention relates broadly to the art of oxide content based on the rubber below approxitreating rubber or rubber compounds and more mately 1% by weight preferred amounts bein particularly to an improved procedure for the around 0.5 part by weight based on 100 parts by vulcanization of certain types of goods in the weight of the rubber. Larger amounts may be 5 presence of an organic accelerator whereby to used but the larger the amount the greater the 5 overcome the tendency to become porous, and tendency to increase the water absorption and without sacrificing other desired properties of the thus decrease the electrical properties after water UNITE product. v a immersion. I

In the art of rubber manufacture, particularly The following example is given to illustrate the as applied to goods which are cured in steam such (invention; the parts being by weight: 10

, as rubber insulated wire, especially the light or Example 1 white variety, it has been found-that thevulcanized rubber coating sometimes becomes porous during the cure. This formation of porosity'is A light colored wire insulation compound wasprepared by mixing the following ingredients:

16 particularly troublesome with so-called 'super- 4 Parts 5 aging types of insulation. Such porosity injures 100-00 the physical arid electrical properties of the insumm? w 1 lation. The superaging type of composition is w 100-o0. characterized by containing much-less sulfur Zmc loo'oo than is commonly used in rubber compounding, cndensate' (an'. 2 0o 20 usually one percent or less by weight basedon tloxldant) the rubber, and a much higher proportion-of sulphur very active accelerating materials thanis cusi fi ggifgg flqumm monosulpmde 2 60 I 'tomary. Rubber compounds are fixed by trade v i 5 specifications for various uses, which specifica s is referred-t0 as stock A in the tests and tions are required to be maintained. This is parthe same stock contain an add d a ount OI ticularly'true in the wire insulation art, in which .5 part of heavy ca a nesiaiS referred to thehighest specifications require the use of the as stock B. v super aging type of compound adapted to curing The stocks wereburiedin talc and vulcanized in steam. This is usually done by burying the in live steam-as known in the insulated wire 30 coated wire in talc or soapstone and curing in live industry. vulcanization was carried out with a steam. 1 15 minute rise to 25 pounds per sq. inch steam One of the objects .of the invention is to prepressure'andlthen held at that P e u r 60 vent the development of porosity in rubber arand 75 minutes respectively with stocks A and B.

5 ticles during vulcanization in steam, particularly Stock A was porous due to blowing during the in insulated'wire stocks which are accelerated vulcanization. Stock B was well vulcanized, solby an organic accelerator of the thiuram sulphide id and free from porosity. The tensiles, unaged class alone or in conjunction with one or more and aged, as well as scorch characteristics of accelerators of other types. Another object of the stocks are given in the table below.

40 the invention, is to provide a means of preventing 40 said porosity without sacrificing other desired Unflgfld physical properties of the product. Other objects will be. apparent from the following description. StockA Stock B It has been found that when magnesiumoxide is combined'in certain small proportions with the E T E 45 organic accelerator in the rubber stock that after the cure in steam, the stock is non-porous and has improved physical properties both before :3: E18 {it 2% and after aging and further that there is no ma- 7 1280 5o terial change in-the scorch characteristics of the stock. Zinc oxide, antimony oxide, antimony Agedm days in oxygen) 4 pentoxide and litharge used in the same and varying amounts did not overcome porosity as 45' 1020 353 1480 450 did magnesium oxide. The objects of the inven- 3g 3% Y 55 tion are best attained by keeping the magnesium 55 others.

T refers to tensile strength in lbs/sq. in, at break; E refers to per cent elongation at break.

Good results have also been obtained with the type of magnesium oxide known to the trade as light calcined magnesia.

Instead of the monosulphide, other thiuram sulphides may be used such as the polysulphides, for example, tetramethyl thiuram disulphide, or di-pentamethylene thiuram tetrasulphide, or Examples of other accelerators that may be used. therewith are the mercaptobenzo thiazoles and their derivatives including such as dibenzothiazyl disulphide.

The thiuram sulphides, however, have been found to serve more efiectually in wire insulation stocks to give goods of the desired characteristics.

Many different embodiments of this invention may be made without departing from the spirit thereof, and it is to be understood that I do not limit myself to the foregoing examples or description except as indicated in the follow-- ing claims.

Having thus described my invention, what I claim and desire to protect by Letters Patent is: s

1. A method of preventing blowing of wire insulation rubber compounds during vulcanization thereof in steam which comprises incorporating therewith, and vulcanizing the rubber coated wire in steam. 2. A method of preventing blowing of wire insulation rubber compounds during vulcanization thereof in steam which comprises incorporating in the rubber stock about .5 per cent by weight of magnesium oxide based on the rubber in adadapted for curing in steam, which rubber portion is characterized in containing besides a thiuram sulphide accelerator, some but not more than approximately 1% by weight based on the rubber of magnesium oxide whereby to prevent porosity during the cure in steam.

4. A rubber insulated wire, the rubber portion of which is of the super-ageing type and normal- .ly adapted for curing in steam, which rubber portion is characterized in containing besides an organic accelerator, some but not more than approximately 1% by .weight of magnesium oxide based on the rubber whereby to prevent porosity during the-cure in steam.

5. A rubber insulated wire, the rubber portion of which is of the super-ageing type and normal- 1y adapted for curing in steam, which rubber portion is characterized in containing besides an organic accelerator, some but not more than approximately 1% by weight of calcined magnesia based on the rubber whereby to prevent porosity during the cure in steam.

6. A rubber insulated wire, the rubber portion of which is of the super-ageing type and 'normally adapted for curing in steam, which rubber portion is characterized in containing besides an organic accelerator, some but not more than approximately 1% by weight of heavy calcined magnesia based on the rubber whereby to prevent porosity during the cure in steam.

ERNEST B. CURTIS. 

